An unexpected disease journey


This is an FYI post, I recently had an unusual disease situation/outcome and felt like I should share it because it was unusual. It primarily affected corys so that's why I'm putting it in the cory forum. It'll be a little long because I want to include as much info as possible. For the TL;DR version, scroll down and start just below the last video link.

First the tank's history - I have a planted 40-breeder tank that I set up in March. The filter is a SunSun 304B 100-gallon, that has been running on a different tank for a couple of years already (so, mature and cycled when I put it on the 'new' tank.) There's also a large sponge filter that had been matured in the same existing tank prior to the move.

The previous tank only had a pair of red swordtails in it, and they moved over to the new 40g tank with the filter(s). I brought in a second female swordtail from my livebearer pool, and a male barbatus cory. The substrate was new (play-sand), added some new driftwood that had been soaking in a bucket for several months, and some rocks in one corner for a fry sanctuary (rocks also came from the previous tank.) Ordered some plants, and moved some others from other tanks, and they all went in within that first week. Moved some shrimp in, and some also came in with the filter. Snails came in with the plants and/or filter (my own plants, not the ones I purchased.)

Maybe a week later, I added 8 loxozonus corys that had been waiting in quarantine, and at the end of April I also added a female barbatus cory that had been in quarantine. She was the last fish added to that tank, and other than water/food, root tabs for the plants, and swordtail fry born in the tank, nothing else had or has been added since the end of April.

Pic of the tank:


Everything was great through May and June. The barbatus female matured, and they started spawning around the end of June. The only issue I had in that time was that the loxozonus corys weren't all growing at the same rate; two of them were clearly larger than the rest (they all started off near the same size.) Pic with one of the larger ones for reference:


Never kept these guys before, so wasn't sure what to expect with them. I have had some schwartzis that took a really long time to reach full size, and I've also had a group of melinis that some of them took a long time to grow as well.

In the nature of including everything (because I still can't be certain what is actually relevant) - there had also been a little flashing happening in this tank now and then. Never outside the 'normal' realm, though - one fish might flash once in a given day. Was never any significant number of fish doing it on any given day, nor one particular fish doing it more often either.

I also should note that I don't do 'regular' water changes. I'm Walstad-influenced, so I monitor parameters and do changes when indicated - such as the nitrates getting too high, or if the pH is dropping. My tap water is on the hard side (though not high pH, it's around 7.2 generally, sometimes up to 7.6. High GH but not high KH), and sometimes also has more nitrates than I'd like (I've measured my source water as high as 20ppm before; kinda defeats the purpose of a water-change.)

I finally got my own RO filter because my source water is so variable (I'm outside city limits, I don't think the county is that fussed about monitoring the water), but it's not a high-capacity one so I typically only use it every other water change, to cut the nitrates and mineral content down a bit. [It only processes around 5 gallons per hour, and I don't really have anywhere to collect the RO output water to use later, so a water change using it can take all evening for just one tank.]

Also will mention that I've got 10+ tanks going at home (two10-gal, three 20-gal, a 30-gal, three 40-gal, a 45-gal, and the 250+ gallon pool); mentioned because what happened in this tank didn't happen/hasn't happened in any of the others. I also hadn't done any water-changes in the others during this time, so that may or may not mean anything.

So, now to what happened. I did around a 30% water change on the 40g, not using the RO. Didn't test the source pH, temp was slightly warmer (finger-test) than their tank water. Nobody showed any signs of stress during or right after, and the water change inspired the barbatus to a spawning session as well (even though it wasn't cooler than their tank water, I guess an influx of 'new' water can be enough to trigger them as well.)

The following day, one of the smallest loxozonus corys was hovering in one place mid-water. They do that sometimes, but not for as long as this one was. Didn't think too much about it. Next day or two, a majority of the corys (including both barbatus) had stopped eating and were looking absolutely miserable. The swordtails were unaffected at first, but then they also stopped eating (at least the adults; the juveniles kept eating normally). Still didn't really see anything specific to treat for, and the parameters were okay (0/0/20-30, pH still 7.2), so I just continued to watch them.

The corys went downhill rapidly, all began showing signs that they were having trouble breathing along with now also showing outward signs of bacterial infection (melting barbels, fin erosion), and one of the big swordtails had a white spot on her side that looked like columnaris. So I started treating the tank with Kanaplex. I also took the corys that were having trouble breathing out and gave them baths in MB daily, to help them with the breathing difficulties.

This is how fast they went downhill - these pics of the male barbatus are only a few days apart, the first from July 17th and the second from the 21st. He and the female both died the following day.


Within the next day or two I lost both of the barbatus corys, and 3 of the loxozonus. The remaining loxozonus were all in bad shape; wedging themselves in plants near the surface, skipping along the surface when trying to air-gulp, and the one that started out hovering was still hovering and looking worse every day. None of them had eaten for at least a week by this point. I was pretty sure I was going to lose them all, still with no idea what had even happened. I have never seen a cory doing this (cory skipping across the surface) that survived, and at least 3 of the remaining 5 were doing it.

But I noticed something about the hovering one that I hadn't seen before; its eyes were cloudy. So I started looking up that symptom, and found that parasites could cause it. So I added PraziPro and Ich-X to the Kanaplex I was already treating them with. I wasn't doing water changes during the treatment, because the parameters were still stable and I knew the meds could be used together. I only did the recommended 3 doses (every other day) of the Kanaplex, and I started the other two meds just before the last Kanaplex dose.

I took this video on what I thought was going to be the hovering cory's last day; a fourth loxozonus had died earlier that day, and this one looked to be the next. The hovering cory's fins had gotten a bit better and his eyes were clearing up by this time, but he still hadn't eaten for over a week; and it didn't seem like he was going to be interested anytime soon (even frozen bloodworms hadn't tempted them.) I took the video because I was touched that the biggest of the loxos had gone up and was hovering with him (or her, still too early to really know), gently touching him as if to let him know he wasn't alone. [They are definitely more social than just a 'schooling' fish, a tetra would attack another tetra that was that sick and try to drive it away from the shoal.]

I nearly took him out and euthanized him right then, I really thought it was a goner. But since he was at least a little better outwardly, I decided to give him another day. And when he made it another day, I gave him another. I continued on with the Prazi and Ich-X treatments, minus the Kanaplex because it's recommended to give a break after the first round of it.

The corys kept hanging in there, and every day I was surprised to still come up with four alive when the lights came on in the morning and when I came home from work in the evening. The swordtails were all eating again by this time and the spot was gone from the side of the one, and the biggest loxo cory was even foraging a little again; but the others still weren't eating. The smallest two remaining were painfully thin, so I decided to also throw some Vita-Chem into the water, in hopes that they might at least absorb some vitamins.

And a day or two after that, I took this video.

Foraging again, including the littlest (previously hovering) cory. You can probably see his gills are still open/irritated, and the earlier video of the cory skipping across the surface was also him (and it was taken just after this one), so he wasn't out of the woods yet. But having them all eating again was a very positive sign.

And as of today, all four of them are fine. No breathing issues, no hovering, no skipping across the top. You'd never know anything bad had ever happened to them, other than the littlest one's barbels are still growing back and he's still got a little redness at the gills, plus he and the other smallest one are still too thin. A video taken just now, also interesting that the biggest ones go over and check in with the littlest, maybe to make sure it's going to eat.

What I mainly wanted to share about this are the observations that challenged some of the things that even I have believed in the past. The 'cure' wasn't due to water-changes - because I didn't do any, after the one that (seemed like) started it all. It wasn't from medicated food, because they weren't eating. It wasn't just time, I have no doubt that if I'd just left them alone they'd all have died. And it very much seems like the issue actually was a parasite of some kind, even though the main outward symptoms were of a bacterial infection. Bacteria are ever-present and will attack when a fish is under other stresses; and I did know that a bacterial infection can be secondary to a parasite attack.

I wonder if maybe that happens more often than we realize, because the first/obvious symptoms were of bacterial infection, while it was the anti-parasite meds that seemed to be what helped in the end. Meds that I wouldn't have even thought of trying, except for seeing that one with cloudy eyes; a symptom I knew I hadn't ever seen with columnaris or other common bacterial infections.

I still don't know 'what' parasite, nor do I know how it came in. But I'm pretty confident that the Prazi/Ich-X combo is what turned them around. The Kanaplex did clear up the outward fin-erosion symptoms and the white spot on the swordtail, but the fish didn't start acting like they felt better until they'd been off the Kanaplex for a week and on the anti-parasite meds for over a week.

For the potential that the water change actually did trigger this - I did already know that water utilities don't necessarily eradicate all bacteria/protozoans/etc. They only have to get rid of the ones that affect humans. Most fish parasites and fish diseases are unique to fish, so it's not impossible that they're not treated for, and that they could have come in with the water change that seems to have precipitated all this. The only other likely vector is the loxozonus corys themselves; they were wild-caught, and I didn't really do much other than observation with them in quarantine. A parasite can make it past observation if a fish is otherwise healthy, even a really long observation (I'd had the corys for 3 months by this point.) And with some of them not growing as well, that also made me wonder if a parasite might be the reason. Something stealing nutrients, since they were all eating normally before it happened.

I don't guess I'll ever know for sure, but I'm grateful that I managed to save some of them. And I'm still gob-smacked that any of them made it back from being that far gone.

So it's also an observation that hopeless isn't always hopeless. A cory skipping across the surface like that I would definitely have called hopeless before now, based on my own experience. The main reason I stuck it out with these is that I really had nothing left to lose.


I will agree on the parasite issue. Especially if wild caught. Probably something that doesn't make it to tanks often enough for most to identify easily or at all. Glad you found something that worked, though!


For my reference : Did you remineralize the RO water ?


For my reference : Did you remineralize the RO water ?
No. My tap water is around 180ppm/10dGH, and I'm topping off this particular tank (with a gallon or two of tap water) every 3-4 days right now, because I've got a fan blowing across the top to keep the tank water cooler (increasing evaporation). I don't do any huge changes with the RO, it just takes too long at 5gal/hr. If I get a higher-capacity unit and use it more often, I will look at remineralizing while doing larger changes with it.

I'd expect to see issues with the swordtails first if remineralization was an issue, would expect to see the shimmies after doing a change with the RO. The tank is lightly stocked (3 adult swordtails, right now two juveniles, plus whatever random fry that I couldn't catch and move; and at the time 8 loxozonus (panda-sized and smaller) and two barbatus, in 40 gallons), so wouldn't expect minerals to be exhausted quickly either.

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